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Perhaps the most critical part of the Shuttle's flight is the communications blackout phase of reentry, when atmospheric plasma is directly interacting with the vehicle's heat shield. As I understand it, they had to maintain a 40 degree angle of attack during this phase of the flight, and I'm curious how this was actually achieved through the design of the control surfaces.

  • Were they hydraulically controlled?
  • What were the specifications?
  • How did they prevent plasma from entering through the hinges of the control surfaces?

I'm assuming this phase of the flight required some level of active control here, though it's possible that's incorrect. In this video, they mention "closed-loop guidance" during this phase of the flight.

ijustlovemath
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    All phases of flight had active control. Did you mean manual control? – Organic Marble Feb 07 '24 at 21:57
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    This question is pretty broad, but the answer gives a good overview of all the sub-questions. – Organic Marble Feb 07 '24 at 22:01
  • It doesn't seem much broader than other similar questions! But I'm specifically asking about the control that happens during the "plasma hitting heat shield" phase of the flight (technical term ;) ). If you have suggestions for narrowing the scope, I'd be happy to make an edit – ijustlovemath Feb 07 '24 at 22:31
  • In the early phases of entry the RCS jets played a major role in attitude control. – Organic Marble Feb 07 '24 at 22:58
  • "I'm assuming this phase of the flight required required some level of active control here". In fact even capsules are under active control during the plasma phase of reentry as they control their lift which manages g force and descent rate. In the case of Shuttle, shortly after entry interface it began a series of roll reversal turns to manage the descent rate, and this continued through the entire plasma phase. All of this was computer controlled, although on STS-2 there was brief manual control. When they got to about fighter jet speed and altitude the commander flew it in for a landing. – Steve Pemberton Feb 08 '24 at 15:50
  • Wow, I'd never considered capsules to have active control surfaces! What did they use? – ijustlovemath Feb 08 '24 at 16:48
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    @ijustlovemath, as far as I know, every capsule has used attitude jets rather than mechanical control surfaces, though I've seen proposals for weight-shift control (which turns the entire capsule into a control surface). – Mark Feb 08 '24 at 23:46
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    Am I correct in my impression that, during the period of high reentry heating, the actual forces are comparatively low? – ikrase Feb 09 '24 at 12:01
  • @ijustlovemath - if a capsule comes in with a slight off-axis angle it will generate lift. By controlling the angle of attack they can increase or decrease lift, giving them quite a bit of control over downrange landing distance, as well as a little bit of cross-range capability. As Mark said they did not use control surfaces to change the angle. However using RCS alone would have used too much to hold an angle. The trick is that the capsule's center of gravity is purposely off-center, causing the capsule to tilt. Using small amounts of RCS to roll the capsule they can change the pitch angle. – Steve Pemberton Feb 10 '24 at 03:33
  • @ikrase indeed https://space.stackexchange.com/a/31869/6944 – Organic Marble Feb 10 '24 at 21:37

2 Answers2

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  1. A NASA report says that "Three independent hydraulic systems (APU's) supply power to the surface actuators." The elevons and body flap controlled pitch and thus AoA.

  2. A full list of specifications of these control surfaces might run to hundreds of pages.

  3. Fairings and cove seals "successfully prevented the entry of 1200F hot gases into the wing/elevon joint." That NASA report has more details, and diagrams of the hinges.

  4. https://space.stackexchange.com/a/39136/1235 quotes from and links to a few mission reports, which mention manual flying or autopilot at various stages of descent.

Camille Goudeseune
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    Re: question 2, I'm mostly interested in the broad specifications, eg, maximum force it can reject, material choices, etc. I'm certainly not intending to build one of these in my garage! – ijustlovemath Feb 07 '24 at 22:34
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Supplementary answer regarding the "specifications".

re: Material Choices

The two-segment elevons are of conventional aluminum multirib and beam construction with aluminum honeycomb skins. Each segment is supported by three hinges. Flight control systems are attached along the forward extremity of the elevons. The upper leading edge of each elevon incorporates rub strips. The rub strips are of titanium / Inconel honeycomb construction and are not covered with the thermal protection system. The rub strips provide the sealing surface for the elevon seal panels.

Space Shuttle Press Reference Manual p. 3-21

Organic Marble
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